Modern telecommunication networks are becoming more and more complex. Especially, various types of networks such as global system for mobile telecommunications (GSM), code-division multiple access (CDMA), universal mobile telecommunication system (UMTS), and voice over internet protocol (VoIP) are widely used in daily life. Since these networks are highly distributed and are sometimes connected to each other in a telephone call, factors degrading the quality of speech becomes increased, and the measurement of the end-to-end speech quality becomes very difficult. Thus, the reliable estimation of the speech quality over modern telecommunication networks is very important not only for network system design and development but also for a user of a mobile device.